Parietal bone fragments from fetal mice of late gestation were incised, and fixed with 2.5% glutaraldehyde in 0.2M cacodylate buffer with or without 0.2% tannic acid, and postfixed with 1% osmium tetroxide containing 1.5% potassium ferrocyanide.Electron microsoopic study of bone specimens showed the presence of multilamellar structures(MLS), with a periodicity of approximately 6nm, inside and outside osteoblasts in specimens fixed at pH7.3 with tannic acid. The lamellar structures with in cells were associated with Golgi complexes, endoplasmic reticulum and plasma membrane, while extracellular lamellar structures were located at the periphery of osteoblasts and near, sometimes surrounding, newly synthesiged osteoid matrix. MLS were also found in specimens fixed at pH7.3 but not treated with tannic acid These structures, however, were vesicular and more difficult to find than MLS. The bone specimens fixed at pH6.0 with glutaraldehyde containing 0.1% malachite green contained oildroplets, instead of MLS, inside and outside cells. These ranged in diam from 0.1 to 1.2um and lamellar structures were rarely seen in specimens fixed at pH7.0The chemical nature of MLS in specimens fixed at pH7.3 has not been determined. Preliminary findings suggest that some of these structures may be composed of fatty acids.3.摘出試料は直ちに酸性下にあるグルタールアルデヒド(pH6.0)で前固定,同様のインキュベート,後固定を行なった。これにより,細胞外にまれにODならびにミエリン状の膜構造が観察された。決して細胞内にMLSは観察されなかった。以上の所見から,細胞外で観察されたODは先の報告にあるアルカリインキュベート時に観察された典型的なMLSがpH変化によりODに変化したものを観察したものと推察した。従って,この構造物の本体が,脂肪酸を主体とするものであると考えられた。一方,酸性条件下でも観察された膜構造はリン脂質と推察される。最後に骨芽細胞と脂質代謝,および石灰化との関係が新たに注目される。